Rubber tires are often prepared in a manufacturing process by first building a tire carcass and then building a tire tread thereover. The tire tread is conventionally applied to the tire carcass as a relatively flat, wide, sometimes somewhat contoured, uncured rubber strip which is wound around the carcass with the ends of the uncured rubber strip meeting to form a splice. Tread for retreading is often cut at a 90° angle. The ends of the rubber tread strip for a new tire are usually skived, or cut at an angle other than 90° so that the spliced ends overlap each other. Such procedural constructions are well known to those having skill in such art.
Generally it is desired that the uncured rubber tread strip has a degree of tackiness, sometimes referred to as building tack, so that the tread splice holds together after its construction and is suitable for the subsequent tire cure step. However, the uncured tread strip often does not have sufficient natural building tack for such purpose.
Therefore, an adhesive is often applied to the faces of the opposing surfaces of the tire tread strip splice so that sufficient building tack is present and so that the tread splice can become more securely bonded. For this operation, it is common to apply a solvent based adhesive rubber composition—usually referred to as cement—to one, and sometimes both, faces of the opposing tire tread splice ends.
Examples of various cements for such purpose and tread splices joined by a rubber composition, in general, may be referred to in one or more of U.S. Pat. Nos. 3,335,041; 3,421,565; 3,342,238; 3,514,423; 4,463,120 and 4,539,365. It is readily observed that such exemplary cements are typically based on, for example, solvent solutions of compositions comprised of, for example, a base rubber, hydrocarbon oil, carbon black, tackifier resin and curative.
The tread splice adhesive needs enough cohesive and adhesive strength to hold the tread splice together using only the green tack of the adhesive until curing. Further the circumference of the tire in the tread region can increase slightly in a tire curing press putting a significant strain on the tread splice.
Due to the small adhesion area and large strain potentially applied to a tread splice, adhesives for this application are typically solvent based cements. The solvents increase the molecular mobility of the polymers in the adhesive and increase the wetting of the rubber substrate (e.g., tread ends). Good wetting and molecular mobility promote good adhesion to the substrate. Water based adhesives have replaced rubber cements in some less demanding applications due to their lower volatile organic emissions. The superior performance of solvent based cements often dictates their use, however, so there is a need for cements based on solvents with lower volatile organic emissions.